Field of the Disclosure
The present disclosure relates to a display device, and more particularly, to a backplane substrate of an organic light emitting display device and a method of manufacturing the same, which enables a high gradation even in smaller pixels of a super-high-resolution structure.
Description of the Background
With development of various portable electronic appliances such as mobile communication terminals and laptop computers, there is an increasing demand for flat-panel display devices that may be applied thereto.
As such flat-panel display devices, for example, liquid crystal display devices, plasma display panel devices, field emission display devices, and organic or inorganic light-emitting display devices have been studied. Among these flat-panel display devices, in particular, the application of an organic light-emitting display device is increasing owing to several advantages thereof, such as development of mass-production technology, ease of driving means, a low power consumption, a high image quality, ease of realization of a large screen, and flexibility and etc.
In addition, such a flat-panel display device includes a plurality of pixels in a matrix form and also includes one or more thin-film transistors (TFTs) in each pixel to individually control the respective pixels. Each pixel may include an R-sub-pixel, a G-sub-pixel and a B-sub-pixel for color expression.
However, since a display device for augmented reality or virtual reality needs to realize a high resolution within a limited size, the size of individual pixels is gradually being reduced. In addition, in a display device in which a light-emitting element is provided in an individual sub-pixel, such as an organic light-emitting display device, circuit elements, such as at least two thin-film transistors and one capacitor (2T1C structure), need to be provided in the individual sub-pixel in order to allow the individual sub-pixel to be selectively driven for gradation, and in this case, the respective thin-film transistors have the same structure. However, although element characteristics such as, for example, mobility of the respective thin-film transistors, are improved when the area of the individual sub-pixel is small, a driving thin-film transistor may undergo the saturation of current within a short time when a gate voltage is applied thereto, which makes it difficult to realize various and sufficient gradation.
That is, the higher the resolution, the smaller the sub-pixel, and all circuit elements required to drive each sub-pixel need to be included in the limited area of the sub-pixel. In this case, when the driving thin-film transistor has the same stack structure as the other thin-film transistors, the response time of the thin-film transistors is fast, but sufficient gradation is difficult.